1. Technical Field
This invention concerns the production of hydrogen peroxide vapor and, more specifically, hydrogen peroxide vapor-air mixtures.
2. Background Art
Hydrogen peroxide is used in connection with bleaching, sterilization, and other processes. In particular, for hydrogen peroxide sterilization processes, it is known to break the hydrogen peroxide liquid into particles, e.g., to facilitate subsequent vaporization. See, e.g., U.S. Pat. Nos. 4,296,068, 4,366,125, 4,680,163, 4,707,334, 4,797,255, 4,992,247, 5,152,968, 5,525,295 and British Patent Documents GB 1,582,060 and GB 2,089,213. In U.S. Pat. No. 6,096,265, a film of hydrogen peroxide formed on a porous member is heated to vaporize the hydrogen peroxide, after which the vaporized hydrogen peroxide is mixed with air. (All of the foregoing documents, as well as all other documents cited or otherwise referenced herein, are incorporated herein in their entireties for all purposes.)
For sterilization processes utilizing vaporized hydrogen peroxide, the hydrogen peroxide vapor is often produced by allowing drops of aqueous liquid hydrogen peroxide solution (e.g., 1 to 3 millimeters in diameter) to contact a hot solid surface. See, e.g., U.S. Pat. No. 4,797,255. It is also known to break the hydrogen peroxide liquid into finer particles or a mist. See, e.g., U.S. Pat. Nos. 4,296,068, 4,366,125, 4,680,163, 4,707,334, 4,992,247, 5,152,968, 5,525,295 and British Patent Documents GB 1,582,060 and GB 2,089,213. In some cases, an atomizer (see, e.g., U.S. Pat. No. 5,525,295) or an ultrasonic device (see, e.g., U.S. Pat. Nos. 4,296,068, 4,366,125, 4,680,163, 4,707,334, 4,992,247, and 5,152,968 and British Patent Documents GB 1,582,060 and GB 2,089,213) is used to produce the fine particles or mist.
In some cases, hot air vaporizes the fine particles of hydrogen peroxide to create a hydrogen peroxide vapor-air mixture (see, e.g., U.S. Pat. Nos. 4,992,247 and 5,152,968 and British Patent Document GB 1,582,060); however, the processes of those patents utilize high volumetric air velocity and/or high temperature (i.e., at least 200xc2x0 F., which is over 93xc2x0 C.), even to the point of boiling the hydrogen peroxide particles, and/or can produce only saturated hydrogen peroxide vapor-air mixtures (i.e., the only mixtures that can be produced are those that are saturated with hydrogen peroxide).
Hydrogen peroxide decomposes in the vapor phase (the stabilizers that help prevent its decomposition in aqueous liquid solution do not function in the vapor phase). Thus, for hydrogen peroxide vapor phase sterilization, in which the hydrogen peroxide concentration must be maintained above a predetermined minimum, the hydrogen peroxide vapor is typically produced in xe2x80x9creal timexe2x80x9d (i.e., as it is needed) so that it can be contacted with the articles to be sterilized before decomposition has reduced the concentration below the predetermined minimum. However, because of the significantly different vapor pressures of hydrogen peroxide and water, an ever present problem when producing hydrogen peroxide vapor from aqueous liquid hydrogen peroxide solution is producing a substantially constant concentration of hydrogen peroxide in the vapor phase mixture as a function of time, because differential vaporization may occur.
Thus, the need remains for an apparatus and a method for producing hydrogen peroxide vapor-air mixtures that have a substantially constant concentration of hydrogen peroxide as a function of time and that need not be saturated with the hydrogen peroxide. The need also remains for apparatus and method that allow the production of such mixtures at low air flow rates and at low temperature and whose flow are substantially continuous (e.g., non-pulsating). The need also exists for producing such mixtures that use other carriers (i.e., instead of air) and/or other vaporizable liquids (i.e., instead of hydrogen peroxide).
Method and apparatus that satisfy those needs and provide still other benefits that will be apparent to one skilled in the art have now been invented. Broadly, in one aspect, the invention concerns an apparatus that can produce at high vaporization efficiency from air and an aqueous liquid solution of hydrogen peroxide a substantially continuous flow of a low-temperature unsaturated gas-phase mixture of air and vaporized hydrogen peroxide of substantially constant hydrogen peroxide concentration as a function of time, said apparatus comprising:
(a) a vaporization plenum having an inner surface;
(b) means for breaking the aqueous liquid solution of hydrogen peroxide into fine particles and for flowing the fine particles in the vaporization plenum, the bulk flow of the fine particles flowing in the vaporization plenum being in a first direction;
(c) means for flowing the air in the vaporization plenum and for flowing at least some of the air between the inner surface of the vaporization plenum and substantially all of the fine particles to create a curtain of air between the inner surface of the vaporization plenum and substantially all of the fine particles, the bulk flow of the air in the vaporization plenum flowing in substantially the same direction as the first direction; and
(d) means for causing substantially all of the fine particles to vaporize in the flow of the air to produce a flow of a gas-phase mixture of air and vaporized hydrogen peroxide of substantially constant hydrogen peroxide concentration as a function of time.
In another aspect, the invention concerns a method for producing at high vaporization efficiency from air and an aqueous liquid solution of hydrogen peroxide a flow of a gas-phase mixture of air and vaporized hydrogen peroxide of substantially constant hydrogen peroxide concentration as a function of time, said method comprising:
(a) feeding the aqueous liquid solution of hydrogen peroxide to the means of subparagraph (b) of the foregoing apparatus;
(b) feeding the air to the means of subparagraph (c) of that apparatus; and
(c) operating that apparatus to produce the flow of a gas-phase mixture of air and vaporized hydrogen peroxide of substantially constant hydrogen peroxide concentration as a function of time.
In another aspect, the invention concerns an apparatus that can produce at high vaporization efficiency from a gas or vapor comprising a first substance and a vaporizable liquid comprising a second substance a substantially continuous flow of a low-temperature unsaturated gas-phase mixture of the first substance and vaporized second substance of substantially constant second substance concentration as a function of time, said apparatus comprising:
(a) a vaporization plenum having an inner surface;
(b) means for breaking the liquid into fine particles and for flowing the fine particles in the vaporization plenum, the bulk flow of the fine particles flowing in the vaporization plenum being in a first direction;
(c) means for flowing the first substance in the vaporization plenum and for flowing at least some of the first substance between the inner surface of the vaporization plenum and substantially all of the fine particles to create a curtain of first substance between the inner surface of the vaporization plenum and substantially all of the fine particles, the bulk flow of the first substance in the vaporization plenum flowing in substantially the same direction as the first direction; and
(d) means for causing substantially all of the fine particles to vaporize in the flow of the first substance to produce a flow of a gas-phase mixture of the first substance and vaporized second substance of substantially constant second substance concentration as a function of time.
In another aspect, the invention concerns a method for producing at high vaporization efficiency from a gas or vapor comprising a first substance and a vaporizable liquid comprising a second substance a flow of a low-temperature unsaturated gas-phase mixture of the first substance and vaporized second substance of substantially constant second substance concentration as a function of time, said method comprising:
(a) feeding the liquid comprising the second substance to the means of subparagraph (b) of the immediately foregoing apparatus;
(b) feeding the gas or vapor comprising the first substance to the means of subparagraph (c) of that apparatus; and
(c) operating that apparatus to produce the flow of a gas-phase mixture of the first substance and vaporized second substance of substantially constant second substance concentration as a function of time.
In preferred embodiments, the vaporizing (e.g., carrier) gas or vapor (e.g., air) flows between the inner surface of the vaporization plenum and substantially all of the fine particles of the second substance (e.g., a liquid solution of hydrogen peroxide) to create the curtain of first substance; the vaporizing gas or vapor flows into the vaporization plenum through openings (e.g., holes, arcuate slots) that are symmetrically arranged around an imaginary line; the particles of vaporizable second substance are introduced into the flow of the vaporizing gas or vapor at a point along the imaginary line; the apparatus is oriented so that the bulk flow in the vaporization plenum is up and substantially vertical; an ultrasonic device is used to produce the fine particles from the bulk liquid; the inner surface of the vaporization plenum is substantially parallel to the imaginary line; and the flow of the gas-phase mixture of the first substance and vaporized second substance is substantially continuous.
This invention provides apparatus and method for producing hydrogen peroxide vapor-air mixtures that have a substantially constant concentration of hydrogen peroxide as a function of time and that need not be saturated with the hydrogen peroxide. Moreover, the apparatus and method of this invention can produce such mixtures at low air flow rates and at low temperature. More generally, the apparatus and method can be used with other vaporizing (carrier) gases or vapors instead of air and with vaporizable liquids other than hydrogen peroxide solutions. This invention has still other features and benefits that will be apparent to one skilled in the art.